There was Avebury, the Rollrights and of course the Napalm attack on Men-an-Tol and Lanyon Quoit (I think it was Lanyon).

Hob, I too thought 'Hammer House'!

I kinda hope it was a movie-making prick that did this one. At least then we don't have a copycat paint dauber to contend with who would be likely to strike again.